1. Field of the Invention
The invention relates to an apparatus to multiplexing several laser beams into one spatially coherent beam.
2. Description of the Prior Art
Because there are practical limits to the pulse power from a single laser as well as limits to the pulse rates that can be achieved, it is desirable to combine beams from a plurality of separate laser sources into a single beam. Devices for combining beams from a number of sources or for splitting beams from a signle source have generally employed beam splitters of semi-reflecting plates. In the case of beam combining systems, such a plate is used to reflect one beam along a path while allowing a beam from a second source to be transmitted through the plate along the same path. Such devices, however, are inefficient in that the beam splitter cannot reflect all the energy from the one source and transmit all the energy from the other source in combining the two beams. Such devices are especially inefficient when the two beams being combined have equal polarization. Other devices use a series of rotating mirrors or a rotating arcuate mirror surface to combine the pulses; however, these devices tend to degrade the far field irradiance by smearing the beam on the target. Furthermore, their moving parts require accurate alignment, and the devices cannot superimpose continuous beams. Examples of these devices include U.S. Pat. No. 4,154,507 and Japanese Pat. No. 52-11894.